An Excerpt on Acid Rain
It's the newest Weather! Built for poison, loved for poison! No longer will poison be worst attack type in the game: You'll see it on non-poisons, guaranteed!
When one starts the Acid Rain weather, all other weathers are removed and Acid rain rules!
First off, it causes damage to all enemies that aren't bug, grass or poison type. Water and Steel (if not with an immune type) take 12.5% damage while in play (non cumulative on say… Empoleon) and others take 6.25%.
Next, any Poisoned Pokemon instantly has the poison changed to toxic status if they switch into the rain. Steel types can also be poisoned during this time. Water and steel also take Super Effective damage from poison moves. This means that Ferrothorn (Grass/Steel) takes 4x damage from a Sludge Bomb. Beware!
Water moves become poison type (with no change to side effects) during Acid Rain and STAB shifts accordingly.
Gunk Blast never misses
Solar Beam has halved damage.